Over the years. many composites have been developed for reducing loud noise such as noise from heavy machinery, and engine noise from trucks and aircraft.
For example, U.S. Pat. No. 4,056,161, discloses a foam-barrier-wear layer composition which provides noise transmission loss. The outer wear layer can be polyvinyl chloride reinforced with fabric The foam layer can be a low density polyester based polyurethane foam having open cells or pores. The intermediate high density barrier layer comprises a vinyl plastisol composition with a particulate material such as barium sulfate particles dispersed therein. The sound barrier layer also acts as a bonding layer for adhering both the outer layer and the foam layer. This product is used for tractor cab mats, fire wall barriers, headliners. etc.. on heavy equipment vehicles as well as for pipe wrap.
U.S. Pat. No. 4,110,510 discloses a sound barrier material comprised of a polyvinyl chloride impregnated fiber sheet or mat having a rubbery coating of a barium sulfate containing chlorinated polyethylene on each side. The fiber sheet or mat is preferably fiberglass. A foam. preferably polyurethane. having a density of 1.5 to 2.5 pounds per cubic foot is further laminated to one of the coating layers and functions as a decoupler to the mass barrier. This type of product is typically applied to noise enclosures and as pipe wrap for in-plant retrofit.
U.S. Pat. No. 4,340,129 discloses a flexible acoustical laminate construction comprising a weighted polymeric laminate having a surface density of at least about 0.5 lb/ft.sup.2, and, adhered thereto, a polymeric foam composition designed to have a loss factor v of at least about 0.4 at 25.degree. C. This acoustical laminate like the two aforementioned, is a foam-barrier construction (decoupled mass) except that a highly plasticized polyvinylchloride foam is the decoupler rather than open cell polyurethane foam. This material is used, primarily. for cab liners in heavy equipment.
U.S. Pat. No. 4 488,619 discloses a foam-barrier-foam-facing acoustical composite having acoustical and flame retardant properties. The acoustical composite is a multi-layered laminated fabric composed of a flame retardant polyvinyl fluoride facing layer, a fire resistant acrylic adhesive layer bonded to the polyvinyl fluoride facing layer, a first polyimide open cell foam layer bonded to the adhesive layer. a noise barrier layer bonded to the first polyimide open cell foam layer and a second polyimide open cell foam layer bonded to the noise barrier layer.
Previous to August. 1988. the Federal Aviation Administration had regulated, under Federal Aviation Regulation No. (FAR) 25.853, flame requirements for interior materials of FAA certified aircraft. This requirement was a vertical flame test whereby the specimen is exposed vertically to a flame (for 12 seconds under FAR 25.853(b), or 60 seconds under FAR 25.853(a)) and removed.
The average burn length could not exceed 8 inches and the average flame time after removal of the flame source could not exceed 15 seconds. Drippings from the test specimen could not continue for more than an average of 5 seconds after falling.
In August of 1988, in addition to FAR 25.853 (a) and (b), the FAA promulgated regulations requiring that interior materials of manufactured or retrofitted aircraft, in the transport category classifications, had to meet a new flame requirement which is the Ohio State University ASTM E-906 Test, FAA modified. This test records the maximum heat release rate (HRR) and maximum smoke release rate (SRR).
The Ohio State University (OSU) rate-of-heat apparatus. as standardized by the American Society of Testing and Materials (ASTM), ASTM-E-906, was determined to be the most suitable for material qualifications. All large surface materials installed above the floor in compartments occupied by the crew or passengers would have to comply with the new flammability standards. See FAA, 14 C.F.R. parts 25 and 121, Improved Flammability Standards for Materials Used in the Interiors of Transport Category Airplane Cabins: Federal Register, Volume 53. No. 165 (August 25. 1988).
The Federal Register indicates the FAA modifications to the OSU ASTM-E-906 test apparatus. First, 5 thermocouples are used in the thermopile rather than the ASTM E-906 3 thermocouples for more accurate temperature measurement.
Second, a slotted metal frame that reduces the mass of metal in the frame holding the specimen is used for minimizing the heat sink character of the non-slotted metal frame of the E-906 apparatus.
The FAA modifications to the test apparatus method were initiated to reduce the variation in test result values from test to test. (The Ohio State E-906 test was giving 18-20% test result variations while the FAA amended E-906 test reduced test result variations to 6-7%.)
Interior materials of these new or retrofit aircraft, in addition to having to comply with FAR 25.853, would also have to achieve a 100 or less maximum heat release (HRR) of 2 minutes, and at peak when tested to the FAA modified Ohio State University ASTM E-906 test. (FAA OSU ASTM E-906)
In August of 1990. the FAA requirement will tighten to 65 or less maximum heat release (HRR) and will have a smoke density (Ds) of less than 200 when tested to National Bureau of Standards Smoke Chamber, ASTM F814-83.
Present fire block acoustical composites on the market for aircraft noise suppression cannot meet the recent FAA OSU ASTM E-906 flame requirement.
An improved fire resistant acoustical composite needs to be invented to pass the newly regulated FAA flame requirements.